Fix doc comment for get_available_resource
Fix doc comment for get_available_resource

nodename has never been used in this call for the libvirt driver.
Commit 6ef820410a35cc21f6e7b877335c8a074fda51bf incorrectly
changed the doc comment to say it is used. Fix that.

Change-Id: If8b1cc19541bfa13b9752d7d956066e67d365c3f

klmitch/nova,vmturbo/nova,bigswitch/nova,klmitch/nova,rahulunair/nova,CEG-FYP-OpenStack/scheduler,NeCTAR-RC/nova,dims/nova,klmitch/nova,vmturbo/nova,sebrandon1/nova,NeCTAR-RC/nova,mahak/nova,cloudbase/nova,mikalstill/nova,phenoxim/nova,mahak/nova,gooddata/openstack-nova,mikalstill/nova,dims/nova,mahak/nova,Juniper/nova,BeyondTheClouds/nova,rajalokan/nova,cloudbase/nova,bigswitch/nova,cernops/nova,gooddata/openstack-nova,cyx1231st/nova,openstack/nova,jianghuaw/nova,jianghuaw/nova,Juniper/nova,rajalokan/nova,cernops/nova,hanlind/nova,Juniper/nova,sebrandon1/nova,hanlind/nova,rajalokan/nova,rajalokan/nova,openstack/nova,gooddata/openstack-nova,zhimin711/nova,vmturbo/nova,rahulunair/nova,CEG-FYP-OpenStack/scheduler,zhimin711/nova,gooddata/openstack-nova,openstack/nova,rahulunair/nova,BeyondTheClouds/nova,vmturbo/nova,phenoxim/nova,mikalstill/nova,jianghuaw/nova,cernops/nova,klmitch/nova,cyx1231st/nova,Juniper/nova,jianghuaw/nova,sebrandon1/nova,alaski/nova,alaski/nova,hanlind/nova,BeyondTheClouds/nova,cloudbase/nova